In the field of localizing EM sources, such as radar transmitting antennas or wireless communications systems, systems are known that are arranged for determining a propagation direction of a propagating electromagnetic wave, e.g. for surface surveillance applications. Such known systems include receiving antenna configurations wherein an antenna element can be pivoted so as to find an optimal receipt angular position indicating an electromagnetic wave propagating direction. Another known system comprises a multiple number of antenna elements that are arranged in a circle, wherein direction information is determined based on amplitude and/or phase differential measurements. Both systems, however, suffer from inaccuracy in determining the propagation direction of a received electromagnetic wave.
U.S. Pat. No. 6,377,213 discloses an antenna apparatus having a wave arrival direction estimating apparatus, comprising a plurality receiving antenna elements coupled together by a corresponding variable phase shifter. Adjusting the variable phase shifters changes the effective (receiving) directivity of the apparatus.